Food, animal, and vegetable product and by-product processing plants, such as fish processing, red meat processing, pork processing, poultry processing, potato processing, other vegetable processing, gelatin production, rendering plants, dairy processing, other processing plants, such as cooking and breading operations, butter, ice cream, yogurt and margarine production operations, sauce and dressing production operations, etc., produce large amounts of wastewater containing high levels of organic compounds. These organic compounds include proteins, carbohydrates, starches, fats, oils and greases, phosphate and nitrogen containing compounds, and other food related solids and residues.
Dissolved air flotation (DAF), clarification, sedimentation, filtration, and other solids and fats, oils, and grease removal pretreatment/treatment processes are commonly employed to remove these constituents from the wastewater generated by these processing operations. See for instance, U.S. Pat. No. 4,933,087 issued to Markham, Jr. et al., the disclosure of which is incorporated herein by reference. Additionally, food preparation operations (i.e., restaurants, etc.) also generate similar types of food by product materials, and these materials are collected in grease traps and spent cooking oil collection systems. See for instance, U.S. Pat. No. 5,543,050 issued to Roshanravan, the disclosure of which is incorporated herein by reference. The food byproduct materials collected at these food preparation operations also contain various organic and inorganic materials, including proteins, carbohydrates, starches, fats, oils and greases, phosphate and nitrogen containing compounds, etc.
Float, filtered and/or settled material from DAF, clarification, filtration and sedimentation wastewater treatment and pretreatment operations produce a primary float, settled or filtered sludge material. Materials from DAF treatment operations are commonly referred to as DAF skimmings. These and other wastewater treatment/pretreatment operations are disclosed in Wastewater Engineeringxe2x80x94Treatment, Disposal and Reuse, Third Edition, Metcalf and Eddy, Inc., McGraw-Hill, Inc., 1991; Anaerobic Biotechnology for Industrial Wastewaters, R. E. Speece, Vanderbilt University, Archae Press, 1996; and publications from the seminar, Anaerobic Treatment of High Strength Agricultural and Industrial Wastes, University of Wisconsin, Milwaukee, Center for Continuing Engineering Education. The disclosures of these references are incorporated herein by reference.
Treating, recycling, and disposing this food, animal and vegetable byproducts have created a significant challenge for the industries that produce them. These byproducts are typically processed in rendering/protein recovery processes to produce animal feed products and reclaimed oils. Some of these byproducts also end up as waste in landfills, or are land applied as soil amendments.
Although rendering processes can effectively handle these byproducts, these materials can pollute air and water, and corrode rendering equipment. Increased odors and other air pollutants are emitted from rendering plants when processing products containing these byproduct materials. Chemicals used with the wastewater pretreatment/treatment operations generating these byproduct materials can elevate corrosion of the rendering equipment. The products to be treated and/or recovered from these byproducts materials are typically dissolved or suspended in large amounts of water. This requires significant, and in many cases excessive, energy input to rendering devices/processes. The quality of the finished products produced in rendering these byproducts can also be poor, and their content can vary significantly. These variables can significantly increase rendering costs and degrade the overall quality of the animal feeds and oils produced.
Moreover, many of the chemicals used in DAF treatment and other wastewater treatment operations, such as flocculants, coagulants, acids, alkalies, metal salts, etc., are infused into the byproducts/wastes, which further magnify the adverse impacts these byproducts have in rendering operations and animal feed production. Feed quality can be significantly compromised due to the presence of these chemicals in the byproducts, which degrade byproducts and feed ingredients (i.e., encouraging the formation of free fatty acids and/or high peroxide values) or add other non-nutritious and/or toxic materials to the animal feed products produced. Further, other plant chemicals, such as sanitation chemicals, fuels, lubricating and hydraulic oils, degreasing chemicals, heavy metals, dirt, debris, and fecal material, also tend to partition into solids during wastewater treatment/pretreatment operations.
Animal feeds containing these undesirable materials have a limited market and must be sold at substantially discounted prices. In addition, higher quality/value animal feed materials must be commonly blended with the byproduct materials to produce an acceptable quality animal feed material. If the rendering plant is producing pet food grade feed, additional processing equipment is required to handle DAF skimmings and other wastewater treatment solids since pet food manufacturers will not typically purchase any feed ingredients containing these materials. There have also been several instances where these byproduct materials have significantly contaminated animal feed products making them unsafe for use. There have been still other instances where the meat products from the animals fed on feeds containing these byproducts have become significantly contaminated.
Given all these problems, whether potential and realized, there is a strong need for an effective, environmentally friendly, non-rendering type treatment for DAF skimmings and other food solids byproducts. It would be highly desirable to take these byproducts from the xe2x80x9cfood-chain.xe2x80x9d The present invention addresses these needs.
The present invention relates to a system and method that can be used to convert animal, vegetable, and food byproduct materials into useful bio-gas and fertilizer, and/or soil amendment products. The present system and method can be used on site at food, meat, poultry, and rendering plants. The present system and method use anaerobic digestion to break down the fats, oils, and greases, proteinaceous, and carbonaceous substances contained in the byproducts.
Anaerobic digestion creates bio-gas, mainly methane and carbon dioxide, waste biosolids, which can contain phosphorous, nitrogen and other trace minerals, and a liquid effluent with significant ammonia levels. Ammonia, a useful ingredient for fertilizer formulation, can be recovered from the effluent. The solids and the extracted ammonia and/or phosphorous can also be used to make fertilizer and/or soil amendment materials. The bio-gas can be used to fuel various energy recovery devices, such as boilers for steam generation, gas engine generator systems for power generation, etc.
Thus, the system and method according to the present invention can biologically convert food byproducts into useful products, such as bio-gas, fertilizer, and/or soil amendment products.
A system for converting animal, vegetable, and food byproducts into useful bio-gas and fertilizer, according to one aspect of the present invention, comprises, an anaerobic digester, a liquid-solids separating unit, an ammonia stripper, and an ammonia absorption unit. The system can further include a solids processing unit and an equilization tank.
The anaerobic digester digests or breaks down the byproducts and produces bio-gas containing methane and carbon dioxide. The liquid-solids separating unit, which can comprise a centrifuge, receives the digested byproducts from the digester and separates solids from liquid effluent. The ammonia stripper receives the liquid effluent from the liquid-solids separating unit and removes an ammonia component from the liquid effluent as an ammonia vapor. The ammonia absorption unit receives the ammonia vapor from the ammonia stripper and absorbs the ammonia component into an ammonium containing fertilizer solution. The equilization tank conditions the byproducts before the byproducts are introduced into the anaerobic digester to enhance digestion. The solids processing unit dewaters or dries the solids received from the liquid-solids separating unit.
The ammonia stripper comprises at least one set of a surge tank and a column feeding into the surge tank, and an air blower for blowing air into the column. The ammonia component in the liquid effluent is transferred into the ammonia vapor by flowing air through the column while the liquid effluent is circulated from the surge tank through the column. The liquid effluent is circulated through the column in a first direction and the air is directed into the column in a second direction, which is opposite to the first direction.
The ammonia absorbing unit similarly comprises at least one set of a surge tank and a column feeding into the surge tank. The ammonia component in the ammonia vapor is absorbed into the water by flowing the ammonia vapor through the column while the water is circulated from the surge tank through the column. The water is circulated through the column in a first direction and the ammonia vapor is directed into the column in a second direction, which is opposite to the first direction.
According to another aspect of the present invention, the system for converting animal, vegetable, and food byproducts into useful bio-gas and fertilizer, comprises means for anaerobically digesting or breaking down the byproducts and producing bio-gas containing methane and carbon dioxide, means for separating the digested byproducts from the digester into solids and liquid effluent, means for transferring an ammonia component from the liquid effluent into an ammonia vapor; and means for transferring the ammonia component from the ammonia vapor into water to form an ammonium solution.
Another aspect of the present invention includes a method of converting animal, vegetable, and food byproducts into useful bio-gas and fertilizer, comprising: anaerobically digesting or breaking down the byproducts in an anaerobic digester to produce bio-gas containing methane; collecting and storing the bio-gas from the digester; separating the digested byproducts into liquid effluent and solids; transferring an ammonia component from the liquid effluent into an ammonia vapor; transferring the ammonia component from the ammonia vapor into water to form an ammonium solution.
The method further comprises conditioning the byproducts with a conditioning agent to enhance anaerobic digestion before introducing the byproducts into the anaerobic digester; and dewatering the solids after separating the liquid effluent to form a slow release fertilizer compound. The conditioning agent can be one of a magnesium hydroxide and a magnesium oxide, and the slow release fertilizer compound formed is struvite.
The ammonia component in the liquid effluent is transferred into the ammonia vapor by flowing air or steam through the liquid effluent. The liquid effluent is circulated through at least one column filled with packing material in one direction and the air or steam is directed into the column in the opposite direction.
The ammonia component in the ammonia vapor is transferred into water by flowing the ammonia vapor across the water. The water is circulated through at least one column filled with packing material in one direction and the ammonia vapor is directed into the column in the opposite direction.